Separator media for aluminum cells



ilnited States Patent Undue 3,04%,647 Patented Aug. 7, 1962 3,048,647SEPARATOR MEDEA FUR ALUMRNUM CELLS Margaret P. Korver, Breclrsville, andNelson C. Cahoon,

Fairview Park, Ohio, assignors to Union Carbide Corporation, acorporation of New York No Drawing. Filed Feb. 28, 1958, Ser. No.718,141 5 Uaims. (Cl. 136146) This invention relates to improvedseparator means for primary cells utilizing aluminum metal as the anodematerial, a carbon cathode with an oxidic depolarizer, an aqueouselectrolyte, and a paper separator between the anode and the cathode.

A number of disadvantages limits the usefulness of cells having aluminumanodes. One disadvantage of such cells is that they have a relativelyshort shelf life. Another disadvantage of cells using aluminum anodes ascompared with LeClanche cells, is their poor performance under heavy,light and delayed service. Such cells also often leak or crack beforethey are electrically spent. Additionally, cells containing aluminumanodes are subject to the accumulation of oxidic film on the anode,thereby preventing instantaneous response for current when put to use.

It has been found, in accordance with the present invention, that thedrying out of the separator used with dry cell systems using aluminummetal as the anodic material is to a great extent responsive for theabove-enumerated shortcomings of such systems. This is believed to bedue to the fact that in drying out, the separator frequently pulls awayfrom the anode, and does not allow the proper necessary electricalcontact between the separator and the anode of the cell.

It is, therefore, the principal object of the invention to provideimproved separator means for use in dry cells employing aluminum metalas the anode material.

It is a further object of this invention to provide means facilitatingthe application of a separator to an aluminum anode, and therebyincrease the ease of assembling cells using such anodes.

The above objects are attained, in the practice of the invention, by abibulous ionically-permeable colloidal layer next to the aluminum anode.This layer when placed in a cell containing a suitable electrolytebecomes tacky and forms a uniform adhesive bond between the anode andcathode. The colloidal layer in question may be incorporated in cellsusing aluminum anodes in any one of three different ways. In oneembodiment, a colloid film may be placed on the anode, and the mix addedto the cell. Alternatively, the colloid film may be applied to thebobbin before the same is placed in the container for the cell. In thepreferred embodiment of the invention, a colloid film layer is appliedon a paper separator.

The powdered colloids found useful in the practice of the inventionnecessarily are stable-in cell electrolyte, and resistant to chemicaldeterioration in cell environment. Such colloids include locust beangum, gum Karaya, and polyacrylamide resins. Generally, however, anycolloid which is substantially b-ibulous in electrolytes used inconjunction with aluminum anodes, and is resistant to hydrolysis in suchmedium, is operative in the practice of the present invention.

The electrolytes referred to in the preceding paragraph include aluminumchloride, ammonium chromate solutions, aluminum chloride hexahydrate andammonium, sodium or potassium chromate.

Suitably in the practice of the invention the colloidal material issuspended in a resin solution and applied to a paper backing such as aspecial grade of alpha cellulose, which is high in wet strength.

As stated before, application of the separator medium may be made to thesurface of the aluminum anode or to the surface of the barrier sheet orto both. In fact, the aluminum anode coated with a dry anode layer maythen be coated with paper or suitable barrier film, and the whole unitfed to a punch press to prepare individual cell anodeseparator units forcell assembly.

Any binder resin which when used in appropriate amounts permits therelease of the colloid when the anode layer containing such colloid iscontacted with cell electrolyte, is operative. Any solvent in which thebinder resin is soluble and in which the colloid is neither soluble norbibulous to an appreciable degree is satisfactory for applying thecolloid layer to the paper backing sheet or the anode or both.

Examples of resins suitable for forming solution for suspending thecolloids of the invention by dissolving in low molecular weight solventsare polyvinylacetate and polyvinylformaldehyde.

Suitable solvents for the purposes of this invention are acetone, ethylether, ethyl alcohol, chloral, chloroform, cyclopentane, heptane, and,in general, low molecular weight alcohols, ketones and ethers which arecompatible with the selected colloids, resins and cell electrolyte.

In an embodiment of the invention, 9.52 grams of various colloid-formingmaterials were suspended each in a solution of 3.0 g. of polyvinylacetate in -300 cc. of acetone. High wet strength alpha cellulose paperwas coated with each of the above colloidal suspensions to give 300square inches of test separator.

Separators so prepared were placed in an aluminum cell electrolytehaving the following composition:

The relative electrolyte absorption by each separator was measured, andis tabulated in Table I below.

TABLE I Relative Absorption of Various Colloidal Materials in AluminumChloride Electrolyte Locust Hydroxy Poly- Poly- Absorpbean propyl acryl-Methyl vinyl Karaya tion gum methyl amide cellulose alcohol gumcellulose 1 day 1. 74 0. 0795 2. 41 0.1051 0.0618 4. 00

While it is recognized that the composition of the electrolyteinfluences the choice of colloid, considerable variation in theelectrolyte chosen for the aluminum cell is permissible. For example, inan aluminum cell using either MnCl alone or MnCl modified by Na B Olocust bean gum has been found to operate satisfactorily.

A comparison of the service obtained on cells containing theseseparators with cells using plain filter paper as the separator mediumis tabulated in Table II below. It should be noted that all threenumbered lots of cells were prepared from, and contained the samequantities of active ingredients, so that the only variable was theseparator medium. Service values for standard commercial Zinc LeClanchecells of the same size also are given for comparison purposes in thetable. It is apparent from this table that on the very heavy, very lightand all delayed service tests, the film-lined cells of lots 2 and 3excel appreciably. Cells containing filter paper separators perform verypoorly under the same service conditions.

TABLE II Eflect of Separator Medium on the Service of Al-MnO Cells 2.25ohm continuousmin. to 0.65 v. Lot Separator Initial 6 mos. 12 mos.

-1 Filter paper (control) 166 75 N.G. 2 Paper plus locust bean gum 229252 294 3 Paper plus gum Karaya 249 265 N.G. 4 Zinc cells- 210 4 ohmcntinuous min. to 0 75 v. Lot Separator Initial 6 mos. 12 mos.

Filter paper (control) 469 30 N. G Paper plus locust bean gu 479 469 615Paper plus gum Karaya 429 382 471 Zinc cells 7.5 ohm contin- LotSeparator u0us min. to 0.85 v initial 1 Filter Paper (control) 265 2Paper plus locust bean gum 1, 315 3 Paper plus gum Karaya n 4 Zinc cells4 ohm HIFmin. to 1.1, 0.9, 0.8 v. Lot 15 ohm continuous-min. to

0.85 v., initial Initial 6 months 01111112 2.25 ohm LIF 225 ohm int.-hrs./day min. to 0.05 v. min. to 0.65 v. Lot hrs. to 0.9 v., initialInitial 6 months Initial 6 months 64 301 N.G. 21 35 49 355 289 427 355 342 333 357 205 332 Zine cells .n 420 635 4 ohm LIF-min. to 1.1, 0.9, 0.8v.

Lot

Initial 6 months 12 months Leaders uniform tacky contact of the anodewith the cathode is essential for satisfactory output. It is presumedthat drying out of the filter paper separator leads to poor servicemaintenance of cells containing the same. By contrast, good servicemaintenance is obtained with the colloids of the invention, whichprovide a moist, lasting, tacky contact between anode and electrolyte.

In addition to improved cell performance, use of the separators of theinvention increases the ease of aluminum cell assembly. Where previouslysoft filter paper was used as a separator, it presented a problembecause it ripped easily upon becoming Wet with bobbin moisture, andoften caused short-circuited cells. In the practice of the invention,the addition of a colloid to a paper backing tends to give the paper agreat deal more strength.

What is claimed is:

1. In a cell having an anode consisting of aluminum and alloys thereof,a depolarizer and an electrolyte selected from the group consisting ofaluminum chloride, ammonium chromate, aluminum chloride hexahydrate,sodium chromate and potassium chromate, an ionically permeable separatormedium between said anode and said depolarizer, said separator mediumcomprising a c lloid bibulous in said electrolyte and resistant tohydrolysis in said electrolyte, said colloid being selected from thegroup consisting of locust bean gum, gum karaya and polyacrylarnideresins.

2. In a cell having an anode consisting of aluminum and alloys thereof,a depolarizer and an electrolyte selected from the group consisting ofaluminum chloride, ammonium chromate, aluminum chloride hexahydrate,sodium chromate and potassium chromate, an ionically permeable separatormedium between said anode and said depolarizer, said separator mediumconsisting of paper backing having bound thereto a colloid bibulous insaid electrolyte and resistant to hydrolysis in said electrolyte, saidcolloid being selected from the group consisting of locust bean gum, gumkaraya and polyacrylamide resins and being bound to said paper backingby means of a binder resin.

3. The cell of claim 2 wherein said binder resin is dissolved in a lowmolecular weight organic solvent.

4. In a cell having an anode consisting of aluminum and alloys thereof,and an electrolyte selected from. the group consisting of aluminumchloride, ammonium chr0- mate, aluminum chloride hexahydrate, sodiumchromate and potassium chromate, an ionically permeable separator mediumbound to said anode, said separator medium comprising a colloid bibulousin said electrolyte and resistant to hydrolysis in said electrolyte,said colloid being selected from the group consisting of locust beangum, gum karaya and polyacrylamide resins and being bound to the saidanode by means of a binder resin.

5. The cell of claim 4 wherein said binder resin is dissolved in a lowmolecular weight organic solvent.

References Cited in the file of this patent UNITED STATES PATENTS1,201,481 McGall et a1 Oct. 17, 1916 1,807,875 Robinson June 2, 19312,200,301 Ruben May 14, 1940 2,534,336 Cahoon Dec. 19, 1950 2,551,799Hatfield May 8, 1951 2,796,456 Stokes June 18, 1957 2,927,951 LindstromMar. 8, 1960 FOREIGN PATENTS 541,696 Great Britain Dec. 8, 1941

1. IN A CELL HAVING AN ANODE CONSISTING OF ALUMINUM AND ALLOYS THEREOF,A DELOLARIZER AND AN ELECTROLYTE SELECTED FROM TH GROUP CONSISTING OFALUMINUM CHLORIDE, AMMONIUM CHROMATE, ALUMIUNUM CHLORIDE HEXAHYDRATE,SODIUM CHROMATE AND POTASSIUM CHROMATE, AN IONICALLY PERMEABLE SEPARATORMEDIUM BETWEEN SAID ANODE AND SAID DEPOLARIZER, SAID SEPARATOR MEDIUMBETWEEN SAID ANODE AND SAID BIBULOUS IN SAID SEPARATOR MEDIUM COMPRISINGA COLLOID SAID ELECROLYTE, SAID COLLIOD BEING SELECTED FROM THE GROUPCONSISTING OF LOCUST BEAN GUM, GUM KARAYA AND POLYACRYLAMIDE RESINS.